1. Field of the Invention
The present invention relates to a communications system, a presence server and a communications method used for them. Particularly, the present invention relates to a method for forwarding an incoming call to a user according to user presence information.
2. Description of the Related Art
In a conventional Private Branch exchange (PBX), when a user who uses a terminal accommodated in a PBX as one of extension lines uses a call forwarding function of the PBX, the user needs to preset a forwarding destination in the PBX and perform an operation to enable a forwarding state (for example, see Japanese Patent Laid-Open No. 5-316234). Japanese Patent Laid-Open No. 2002-014923 proposes the technology for switching an operation of PBX to automatically forward an incoming call without preset of PBX by a telephone user. In the technology proposed by Japanese Patent Laid-Open No. 2002-014923, a presence monitoring system monitors the presence or absence of user operation of a personal computer (PC) used by a user on desktop. If a user has not operated the computer for a long time, the presence monitoring system determines that the user is absent from one's desk and sends a signal to the PBX to switch an incoming call to the user's telephone from a normal operation to a forwarding state for forwarding it to preset telephone set. Thereby, automatic switching to a forwarding state is achieved without a user operation of PBX.
In Japanese Patent Laid-Open No. 63-301658 and Japanese Patent Laid-Open No. 6-121046, additional technologies about forwarding are proposed. In the technology disclosed in these documents, if a call arrives at an unattended telephone, a PBX memorizes telephone numbers of a caller and a receiver, and calls and connects telephones of the both parties at another time when the both parties are present.
In some of the proposed technologies mentioned above, though switching between on and off of forwarding is automatic, a forwarding destination is fixed. Japanese Patent Laid-Open No. 2005-018194 proposes a technology for dynamically changing of a forwarding destination. In this technology, a PBX retains a user presence status table which indicates user presence (user status) and a per-user forwarding destination table in which a forwarding destination is set depending on user presence in the memory. When a call arrives at a user, the PBX obtains presence of the user from the user presence status table. The PBX obtains a forwarding destination corresponding to the obtained presence from the per-user forwarding destination table, and thereby switches a forwarding destination dynamically.
By the technology proposed by Japanese Patent Laid-Open No. 2005-018194, a forwarding destination can be dynamically changed depending on user presence. However, in this technology, information used for changing a forwarding destination by a PBX is only receiver's presence information. The PBX does not use information of caller side. Thus, in the technology disclosed in Japanese Patent Laid-Open No. 2005-018194, while a forwarding destination and a receiving action can be changed depending on presence of a receiver, there is a problem that a forwarding destination and a receiving action can not be changed depending on situation of a caller.
In particular, even if a caller wants to contact with a receiver urgently, a PBX performs a preset action corresponding to only a receiver's presence without considering a situation of the caller. For example, when, according to a user setting, a prerecorded message is set to be used as a response to an incoming call in presence situation such as when a user is in a meeting or traveling, the PBX responds to the incoming call to a user in such a situation by playing the prerecorded message in the same way even if a caller is in any situation.
In recent years, there are more and more systems in which a PBX accommodates a mobile telephone using a wireless communications system in addition to a desk telephone. A mobile telephone allows a user to call even if the user is away from one's desk. In such a system, a user can operates a mobile telephone to switch an action for reception to a call hold, forwarding, or the like. However, also in this case, a function of PBX which a user can switch is only a receiving action which supports a receiver's convenience but does not identify a situation of a caller.